Grid-tie with power backup combines a grid tie installations with a bank of batteries. Unlike a standard grid-tie system, however, a battery bank provides contingency for power cuts – so that one can continue to use power from solar.

Need for Battery

Batteries are a key component in a grid-tie with back-up or a stand-alone renewable energy system that all of the other components rely on for operation. Without proper maintenance, batteries can fail prematurely and shut the whole system down. The "Best" battery for a particular system is not always the most expensive, but it is seldom the cheapest either. You need to know what your battery storage requirements are.

This type of system incorporates energy storage in the form of a battery to keep “critical load” circuits in the house operating during a utility outage.

When an outage occurs the unit disconnects from the utility and powers specific circuits in the home. These critical load circuits are wired from a subpanel that is separate from the rest of the electrical circuits.

If the outage occurs during daylight hours, the PV array is able to assist the battery in supplying the house loads. If the outage occurs at night, the battery supplies the load.

The amount of time critical loads can operate depends on the amount of power they consume and the energy stored in the battery system.

A typical backup battery system may provide about 8kWh of energy storage at an 8-hourdischarge rate, which means that the battery will operate a 1-kW load for 8 hours. A 1-kW load is the average usage for a home when not running an air conditioner.

Typical System Components:

In addition to components, a battery backup system may include some or all of the following:

batteries and battery enclosures

Battery charge controller

separate sub-panel(s) for critical load circuits

The advantages and disadvantages of a battery based grid-tied system include the following: